Ad hoc networks are spontaneous wireless networks that do not rely on any particular communications infrastructure. The terminals of these networks, referred to below as nodes, have a two-fold role: to use the network for their own requirements and to contribute to the connectivity between the nodes of the network. These networks are referred to as cooperative networks because the nodes thus serve simultaneously as terminals and as routers for the requirements of other terminals. As used below, the term “route” refers to an ordered list of nodes for routing packets of data between a source node and a destination node. In such networks, a packet of data can be routed by the source node, i.e. the source node combines with a packet to be transmitted the route that the packet must take.
This type of network relies on mechanisms of mutual trust between the nodes. However, a node that is part of a route might prove to be relatively uncooperative or even malicious, and interfere with the routing of packets of data to a greater or lesser degree. Thus reputation management techniques have been proposed for this type of network. A first technique, as described in the paper by S. Marti, T. J. Giuli, K. Lai, M. Baker, “Mitigating Routing Misbehavior in Mobile Ad Hoc Networks”, published in the proceedings of the 6th annual ACM/IEEE International Conference on Mobile Computing and Networking 2000, enables each node to supervise the transmission of a packet. When a node receives a packet of data from a source node and to be transmitted to an adjacent node, it transmits it to the adjacent node and, by monitoring the radio channel, it verifies whether that node has forwarded the packet to a subsequent node. If the number of packets not forwarded by that adjacent node exceeds a threshold, the adjacent node is considered malicious and a message is sent to the source node to report the malicious nature of the adjacent node. The same paper also describes a method of administering a trust database that relies on observation of a route. That method requires a protocol for routing by the source. The trust database stores a score for each known cooperative network node, which score identifies the node's contribution to the operation of the network. When a route is valid and being used, the source node periodically updates the scores of the nodes of the route. If, on sending a packet, the route is no longer valid, the scores of the inaccessible nodes are decremented. The node then uses its trust database to select the most reliable route to be used for transmitting packets of data between itself and a destination node.
An alternative technique is proposed in the paper by C. Jensen, P. O'Connell, “Trust-Based Selection in Dynamic Source Routing”, published in the proceedings of the iTrust 4th international conference, May 2006. When a destination node reports to the source node by means of an acknowledgement that a packet of data has arrived correctly at its destination, the source node increases the trust index values of all the nodes of the route; if not, they are reduced. Thus the source node can calculate a trust index associated with the route as a function of the trust indices of all the nodes of the route, and can select a route as a function of parameters including the trust index.
Thus each source node administers its own trust index database. It must therefore select routes on a trial and error basis, with the possibility of making a bad choice including a malicious node, and it must trust its own experience. As a result of this, selection of the route by the source node is unreliable. There is therefore a need for a technique for use in a cooperative network for ensuring the reliability of a mechanism used by a source node to select routes between the source node and a destination node.